Sigma 105mm f/2.8 EX DG OS HSM - £700
Wide-open results are great, and it just gets better from there. That it can come so close to matching the results from the Zeiss is amazing.
Again, second only to Zeiss. There's little central fringing at all apertures, and at the edges it's still better than some lenses at the centre.
A stellar performance, with the best control over distortion out of all the lenses on test, and practically no distortion in real-world images.
Image test verdict
The Sigma lens is consistently sharp, and there are no issues with distortion or chromatic aberration. Its only failings are weaker wide-open results.